Frame-type automatic sprinklers are well known and have been widely used as ceiling sprinklers in all types of environments. Generally speaking, a frame-type automatic sprinkler includes a sprinkler body having an outlet on one side and a closed frame extending from the sprinkler body around the outlet. A plug is received in the outlet. A heat-sensitive element extends generally between the plug and the frame, biasing the plug into the outlet. The heat-sensitive element changes physical form when sufficiently heated to release the plug from the outlet. The element is typically a frangible, alcohol-filled, glass ampule which breaks but may be an alloy with a low melting point. The outlet, plug and heat-sensitive member are generally axially aligned with one another and with an adjustment screw extending through the frame. The screw adjusts the load that is applied to the plug by the heat sensitive element to resist the pressure of the water or other fire-retarding fluid to be delivered to the sprinkler.
Frame-style sprinklers are often installed in residential and commercial locations where aesthetics are a consideration. To improve the appearance of such sprinklers, covers are sometimes provided to conceal the sprinkler and the ceiling opening while the sprinkler is not operating. During a fire, the cover must drop away from the sprinkler, at least by the time the sprinkler activates, so as not to interfere with the delivery of water or other fire-retarding fluid from the sprinkler.
One approach which has been widely used for supporting a cover from such sprinkler has been to provide an outer housing or yoke about the frame of the sprinkler and supporting a cover from that outer housing or yoke. This is shown, for example, in U.S. Pat. Nos. 3,393,746, 3,998,273, 4,014,388 and 4,706,759. U.S. Pat. Nos. 3,727,695 and 4,215,751 disclose variations on this theme where a flange is provided between the frame and the sprinkler body with which an elongated cover member engages.
Both types of mounting have the disadvantage of being particularly bulky. The former typically requires a larger opening to receive the housing or yoke, which must be extended around the frame of the sprinkler. The latter requires a tall cover or cover with tall bracket arms which can extend above the frame of the sprinkler to engage the flange. Again, the ceiling opening must be sufficiently enlarged to receive the cover and/or its arms.
One approach which has recently been introduced has been to provide a cover with a ceiling plate and a pair of centrally located, opposing, transverse bracket members. Each bracket member is made from metal alloy with heat-activated "memory". Each of the bracket members has a pair of spaced, upstanding arms, each arm having an upper edge turned inwardly towards the center of the cover. The inwardly-turned edges can be snapped over a circular deflector which is typically provided on frame-style sprinklers, supported on a lower side of the frame. When the cover is heated to a sufficiently high temperature, the memory of the alloy of the bracket members causes the bracket member arms to deflect radially outwardly, releasing the arms and cover from the deflector. The temperature-sensitive element used to trigger the activation of the sprinkler is then exposed to the heated gases to which the cover was previously exposed.
This approach offers the distinct advantage of compact size and simplicity. However, the alloys required to construct the cover are considerably more expensive than the materials such as copper, brass, plastic, etc., commonly used to construct such a cover. Moreover, there is always the possibility that the deflections "memorized" in the alloy may change over time, due to an exposure to environmental conditions and/or natural changes occurring in the alloy. The failure of such a cover to release at the proper temperature can totally negate the effectiveness of the sprinkler.